The semiconductor industry is continually seeking new ways for improving and increasing the speed of integrated circuits. One method currently employed by the semiconductor industry is the process of making copper interconnects on integrated circuits, rather than the former method of using aluminum interconnects. Copper interconnects provide the advantages of faster speed and better heat dissipation in integrated circuits. The use of copper, however, presents certain problems in the fabrication process. In particular, the wastewater generated from the fabrication process contains copper instead of aluminum, making the wastewater toxic.
The process to create copper interconnects has the following basic overall steps. First, copper is electroplated in and over the trenches of the integrated circuit. The excess copper (outside of the trenches) is removed with a process termed Chemical Mechanical Polishing (CMP). CMP is a hybrid process where copper is polished off the wafer by a combination of chemical etching and physical polishing by fine aluminum oxide slurry. The particle size distribution of the slurry ranges generally from 0.02 micron (200 Angstroms) to 0.10 micron (1000 Angstroms). The rinsing wastes from both of these processes contain variable amounts of dissolved copper.
The rinsewater from the electroplating process is very similar to rinsewater found in plating and circuit shops where copper is plated on metals and circuit boards. In particular, the rinsewater contains dissolved copper salts such as CuSO4, dilute acid, surfactants and dilute levels of other organic and inorganic enhancing agents. The rinsewater from the CMP process contains solids, chelating agents and oxidizers, and presents a significant challenge for waste disposal efforts.
The primary goal for waste disposal of the rinsewater from the CMP process is the removal of copper from the waste stream, without requiring the removal of the solids or oxidizing agents. While ion-exchange is an efficient technology to achieve copper removal, conventional ion-exchange resins would be damaged irreversibly when oxidizers are present. Further, flow patterns of conventional resin columns would cause the solids present in the rinsewater to plug the columns. Additionally, while activated carbon is often used to eliminate oxidizers because it acts as a good reducing agent, the pores of activated carbon particles are susceptible to plugging due to the particle size distribution of the CMP slurry waste.
Accordingly, there remains a need to provide a new and improved method for removing copper present in industrial wastewater streams, and in CMP slurry in particular. There is a further need for unique materials and methodologies for abatement of copper and/or recycling of the wastewater from industrial chemical processes. Additionally, there is a need for an apparatus for use with the methods of the present invention for the removal of copper and the treatment and processing of wastewater from copper CMP manufacturing processes. The present invention is directed to meeting these needs.